1. Field Of The Invention
The present invention relates to a method for increasing the yield of crops by application of a granular fertilizer having a relatively high nitrogen and sulfur content. More particularly, the invention pertains to the use of a N-S granular fertilizer containing urea and ammonium sulfate in specific proportions to increase the yield of rice and other field crops.
2. Description Of The Prior Art
Rice, the cereal grass Oryza satira, is one of the most important food crops cultivated throughout the world. The starchy edible seed of rice provides the principal food for millions of people whose diet depends on its availability. The continued increase of the world's population and concomitant food shortage increase the need for improvements in the production of this staple crop.
The proportion of rice grown in the United States relative to worldwide rice production is small but is steadily increasing, especially in Texas, Mississippi, Louisiana, Alabama and Tennessee. Recent increased cultivation of rice in the southern USA may be attributed to the widespread use of herbicides and pesticides which are utilized to eliminate unwanted weeds and insect pests. Unchecked weed growth, for example, can cause a significant decrease in crop yield and reduce profits for the farmers. However, it can be appreciated that extensive use of herbicides and pesticides increases the overall crop production costs and undesirably affects water quality and wildlife. In some areas, water from rice farms treated with pesticides is discharged into other bodies of water to create environmentally unsafe conditions. In fact, legislation has been enacted in some of the southern states to control discharges of water from such chemically treated areas and to reduce or eliminate the use of these environmentally hazardous chemicals.
The conventional method of producing paddy rice in the United States is to aerially broadcast the rice seed over pre-cultivated and pre-flooded paddies. The rice paddy is normally flooded to a water level of one to four inches in depth prior to planting. Alternatively, a standard grain drill may be used to plant rice seeds into the upper section of the soil, prior to irrigation flushing or flooding with water. The water level is maintained throughout the growing season, except for brief periods when the paddy is drained to allow any required herbicide or pesticide treatment. After germination and emergence of the seedlings, the rice plants grow above the water level in the paddy. These procedures can be modified by soil cultivation after planting, transplantation of rice seedlings and by deeper flooding, which significantly reduce the use of herbicides and pesticides.
Currently, after planting and before germination, a fertilizer is usually applied to the rice paddy, either aerially or with equipment pulled by tractors. A nitrogen-containing fertilizer in amounts of 100 units or more per acre is generally incorporated into the soil. A starter fertilizer containing phosphorus is also often used. In former years, natural fertilizers such as manure composts were used in rice farming, but a reduced yield usually resulted and regulation of the harvest time was difficult to achieve. Over the years, urea (46% N, 0% S), monoammonium phosphate (12% N, 614 P.sub.2 O.sub.5, 0% S), diammonium phosphate (21% N, 52% P.sub.2 O.sub.5, O% S), triple superphospahte (46% P.sub.2 O.sub.5, O% S) and various N-P-K solutions have been tried for fertilization of rice crops. However, these sulfur-free fertilizers fail to replenish the sulfur content of the soil removed with each harvest of the rice crop. The S-nutrient content of the soil is also lost from leaching-out processes that occur during preparation of the rice paddy. The end result is a serious shortage of sulfur in the soil, which is harmful to the rice crop. Further, nitrogen-free dressings of superphosphate (20% P.sub.2 O.sub.5, 12% S) are ineffective by themselves for sustaining crop growth and generally provide the soil with more sulfur than is needed for growing rice. A better supplier of sulfur is ammonium sulfate (21% N, 24% S) since the sulfur is available in a form that can be readily taken up by the rice plant. However, nitrogen-containing ammonium sulfate, by itself, is ineffective for fertilizing purposes by reason of its low nitrogen content and relatively high sulfur content.
While many such natural and synthetic materials are known in the prior art for fertilization of field crops, there remains an important need for the development and application of selective fertilizers which are not only effective in artificially initiating and sustaining rice crop growth, but increasing the yield of this important food crop.